The goal of this project is to maintain and expand a comprehensive epidemiologic surveillance system which will monitor HIV infection and related behaviors among intravenous drug users (IVDUs) and their sexual contacts in Worcester, Massachusetts and its environs, a large urban area where HIV antibody prevalence is still relatively low, and where public health interventions have been collaboratively planned. This project will take place in the context of the Worcester AIDS Consortium which is a formal network of all public and private health, drug abuse treatment, criminal justice and community support system organizations and institutions located in or providing services to an estimated 3,000 needle users in greater Worcester, Massachusetts. Worcester (pop. 175,000) is the second largest city in Massachusetts and New England. The Consortium coordinates priority access to drug abuse treatment, antiviral therapies and community support and advocacy for HIV+ IVDUs. The primary research methodology will be epidemiological surveillance, through the establishment of a anonymous and confidential computerized data base of needle-users and those individuals who, although not themselves needle users, have had sexual contact with needle users, based on data collected in an encounter form to be administered at multiple outreach sites including those interviewed "on the street", and to homeless in shelters in conjunction with individual counselling on AIDS risk reduction and voluntary HIV antibody tenting. Validation methods will be developed to evaluate the completeness of ascertainment of the target population. Indirect surveillance methods will also be employed, to monitor trends in phenomena related to needle-use, such as hepatitis B case reports. Ethnographic studies will be a major component of this research.